NORTON – Keith Gazaille makes a living putting chemicals exactly where it seems most unnerving for them to be: water.

On Wednesday, Gazaille and his team from Shrewsbury-based SOLitude Lake Management loaded up an airboat with a couple dozen containers each filled with 20 pounds of the aquatic herbicide SonarOne.

The chemical pellets SOLitude dropped in the Norton Reservoir that morning will be absorbed by two non-native plants that are invading the 580-acre ecosystem, eventually leaving them bleached and dead at the roots.

“I don’t think anybody goes in and takes any of the approaches lightly,” said Gazaille, SOLitude’s regional director and senior biologist. “All of the techniques have some level of non-target impact.”

Massachusetts cities and towns routinely deploy herbicides in the fight against invasive species that threaten plant and animal life in water bodies throughout the state.

The number of aquatic herbicide applications has been trending upward in recent years, with 295 permits in 2013 and 328 permits last year, according to information provided by the Massachusetts Department of Environmental Protection.

Herbicides are the cheapest and often most effective tool available, but the idea of introducing chemicals into the natural environment – especially near sources of drinking water – puts some people on edge.

The Conservation Commission in at least one MetroWest community – Sudbury – prohibits their use altogether, preferring to harvest invasives by hand and machine.

State and local officials, industry professionals and some nonprofits advocates, however, say herbicides are safe, heavily regulated, and in many cases necessary to preserve water ecosystems.

“It’s possible for the politics of this to really tie things up in knots,” said Mike Lowery, a member of Wayland’s Surface Water Quality Committee. “And while things are tied up in knots, the lakes get worse and worse and worse.”

Thirteen years ago, water chestnuts clogged Carding Mill Pond in Sudbury. At night, the invasive plants would absorb unnatural amounts of oxygen from the water, leaving too little to go around.

“And if you walked around the edges of the pond, you would see fish kill,” Hop Brook Protection Association President Frank Lyons recalled.

Water chestnuts, milfoil and fanwort are some of the most common invasive aquatic plants in Massachusetts. Outside their native environment, the species are able to grow out of control.

The invasives can dominate entire water bodies, killing off native plants and fish and inhibiting human recreation. They can grow so dense on the water’s surface that they block all sunlight from organisms below.

“Invasive species out-compete native species, and having a monoculture doesn’t provide great habitat for wildlife,” said Kim Burlingame, Framingham’s assistant conservation administrator.

Herbicides are rarely, if ever, the only weapon against invasive plants. Hand-pulling, mechanical surface harvesting and diver-assisted vacuum harvesting are other common techniques.

It’s very difficult to fully eliminate infestations, but they can be successfully managed through multi-year efforts. Any seed and plant fragments left behind grow anew the next year.

“We look at the exact plants and the pond conditions in making a determination of which of several treatment techniques are used,” said Jonathan Yeo, director of water supply protection for the state Department of Conservation and Recreation.

DCR tries to minimize treatment on any water body, Yeo said. “Prevention and early detection is really, for us, the most important thing,” he said.

The solutions

The Hop Brook Protection Association uses $10,000 to $20,000 in Community Preservation Act money every year to harvest invasives from ponds in Sudbury. Sometimes, volunteers go out in boats to handpick weeds.

“The problem is you start putting chemicals in these ponds and you don’t really know what the full extent of the damage they are going to do is,” Lyons said.

Despite such concerns, town officials in communities that regularly use the chemicals say they closely monitor their water bodies and have never found adverse effects from herbicide use.

“We’ve never had an issue with fish kill or anything out of the ordinary,” said Vincent Roy, director of public works in Upton, which does a $25,000 herbicide treatment on one pond every three years.

Under state law, local conservation commissions have the authority to approve or deny the use of herbicides in wetlands – but aquatic chemicals face years of federal and state review before reaching that point.

Manufacturers typically spend 10 years developing and studying aquatic herbicides before receiving approval from the U.S. Environmental Protection Agency, which then sets restrictions on their use nationwide.

In Massachusetts, the state may place additional restrictions on particular herbicides when first registering them through the multi-agency Pesticide Board, a process than can take another one to two years.

“And that is something that Massachusetts has but many other states do not have,” said Hotze Wijnja, an environmental chemist for the Department of Agricultural Resources.

Only applicators licensed through the state are allowed to apply aquatic herbicides. In Massachusetts, SOLitude Lake Management dominates the market following its 2014 merger with two other companies doing the same work.

SOLitude’s Gazaille said some people might have “an immediate visceral reaction” to putting chemicals in water, but that existing scientific data doesn’t support concerns about toxicity.

“And that’s not to say there is no risk whatsoever. But used in compliance with the product label, I think that most all of these products, that there is negligible risk to humans and the environment,” Gazaille said.

SOLitude biologists monitor water bodies before and after herbicides are introduced, Gazaille said. The chemical used in Norton this past week, fluridone, was deployed in such a low dose it won’t have lasting impacts on native plants, he said.

“They may be stunted in growth because of the herbicide application, but they will certainly survive and be in good health,” he said of the native plants.

The company, which works in multiple states, also helps towns with physical removal and recommends strategies for long-term solutions, such as ways to manage phosphorous pollution that spurs plant growth.

Some herbicides are approved for direct application to drinking reservoirs, while others are considered safe even if drinking wells are nearby.

"These chemicals, they don’t last for very long and they are not going to migrate down deep into the groundwater to get to a public water supply well," Yeo said.

Striking a balance

Even though herbicide products are considered safe, the state and some individual towns still try to minimize their use.

For years, milfoil dominated upward of 150 acres of Lake Cochituate every summer. A group of Natick residents objected to herbicide use there, but the parties eventually reached a compromise.

The Department of Conservation and Recreation now only has its contractor, SOLitude, use herbicides if invasive plants reach a certain density threshold. Otherwise, physical methods are used.

“It’s early in the season, but we just scoured the entire lake and literally found five single milfoil plants in the entire lake system,” said Tom Flannery, an aquatic ecologist with DCR, holding up the approach as a success story.

Nearly a decade ago stakeholders in Wayland adopted “a model of herbicide minimization” similar to the strategy now in effect for Lake Cochituate, Lowery said.

“We had to pull a group of people together and get them to agree and understand,” Lowery said. “You have a huge population of plants, you need to get it under control before you can stop using herbicides.”

Dudley Pond is effectively kept clear of invasives that interfere with recreational activities, and the use of herbicides has declined over the years, Lowery said.

“The largest problem of controlling invasive weeds is often a political problem,” Lowery said. “The politics is as important as the plant.”

Jonathan Dame can be reached at 508-626-3919 or jdame@wickedlocal.com. Follow him on Twitter @DameReports